1. Field of the Invention
The present invention relates to a disc clamping device having a center hole, and more specifically, to a disc clamping device for clamping ultra-precision disc to which information is magnetically or optically recorded for inspection or movement.
2. Description of the Prior Art
In an ultra-precision disc to which information is magnetically or optically recorded, information recorded to a recording medium on a disc surface is read by a scanning head while the disc is rotated about the opening of a center hole. The interval between the disc surface and the scanning head is made narrower than several micron meters due to the recent increase of recording density. That is, even slight unevenness is not permitted on the disc surface and further discs having various diameters are made to cope with a wide variety of appliances. In the manufacture of discs, although the flatness and unevenness of the surface of them are inspected after each manufacturing step or after a final manufacturing step by clamping the discs, the application of even slight stress to the discs is not permitted in the inspection.
From the circumstances mentioned above, an inspection jig has been devised in a conventional disc clamping device. Japanese Unexamined Utility Model Publication No. 64-37971, for example, discloses a handling jig comprising at least one V-shaped groove part (main body piece) which is fixed to an end of a cylindrical shaft main body and abutted against the outer peripheral edge of a disc, a plunger slidingly disposed in the shaft main body, a shaft fitted to an end of the plunger, a V-shaped groove part (extreme end piece) attached to an end of the shaft and pressed against the peripheral edge of the center hole of the disc and a spring accommodated in the shaft main body and urging the V-shaped groove part (extreme end piece) to the V-shaped groove part (main body piece) side by the pushing motion of the plunger.
Japanese Unexamined Utility Model Publication No. 3-106518 discloses a jig comprising a roller having one V-shaped groove for clamping the center opening edge of a disc, a roller having two V-shaped grooves for clamping the outer peripheral edge of the disc and a clamping part for coupling both the rollers.
The former jig cannot cope with discs having various diameters because the V-shaped groove part (extreme end piece) which is attached to the extreme end of the shaft is fixed. In addition, since there is a possibility that the shaft turns, when a disc is clamped in the turnable state, there is a possibility that the disc is warped or scratched. The latter jig cannot also cope with discs having various diameters because the rollers are fixed to the clamping part. Further, there is a possibility that the clamping part turns.